Liquid displacement gas recovery system for electron radiography imaging chamber

ABSTRACT

Process and apparatus for providing imaging gas under pressure to the imaging chamber of an electronradiographic system. A pump for providing a flushing liquid under pressure to the imaging chamber for flushing air to exhaust, and a source of imaging gas under pressure for flushing the liquid from the chamber and for charging the chamber, with the pump and liquid also flushing the imaging gas from the chamber after an exposure for recovery of the imaging gas under pressure.

United States Patent Lewis et al.

[ 51 Sept. 17, 1974 LIQUID DISPLACEMENT GAS RECOVERY SYSTEM FOR ELECTRON RADIOGRAPHY IMAGING CHAMBER Inventors: John Henry Lewis, West Los Angeles; Arthur Lee Mo'rsell, Tarzana; Murray Samuel Welkowsky, Los Angeles, all of Calif.

Assignee: Xonics, Inc., Van Nuys, Calif.

Filed: July 23, 1973 Appl. No.: 381,862

US. Cl. 250/315, 250/323 Int. Cl. G031) 41/16 Field of Search 250/315, 315 A, 323

References Cited UNITED STATES PATENTS 2,692,948 10/1954 Lion 250/315 3,774,029 6/1972 Muntz et al 250/315 Primary Examiner-James W. Lawrence Assistant Examiner-B. C. Anderson Attorney, Agent, or Firm-Harris, Kern, Wallen & Tinsley ABSTRACT 8 Claims, 1 Drawing Figure G4 zassevom V4002 COLL ECTUQ POWEE 1? JUPP/J/ KESE VO/E F PMENIED 85H 11914 VRPOQ cox. L 5c rag G/QJ' 555 4 vane 1 LIQUID DISPLACEMENTGAS RECOVERY SYSTEM FOR ELECTRON RADIOGRAPHY IMAGING CHAMBER tion. In such a system, an X-ray opaque imaging gas at high pressure is used between two electrodes in an imaging chamber to produce a photoelectric current within that chamber as a function of X-rays entering the chamber. The current iscollected on adielectric receptor sheet placed on one of the electrodes, resulting in a latent electrostatic image on the receptor. The latent image is then made visible by xerographic techniques.

A 14 by 17 inch electron radiography imaging chamber has a volume between the electrodes of nearly one liter. The X-ray sensitive imaging gas is pumped into this volumeto a pressure of 20 atmostpheres or more. The gas is much too costly to discard after each exposure; yet between exposures it is necessary to openthe chamber to transport the exposed receptor to a development station and insert a new receptor. The obvious solution is topump the gas out of the imaging chamber into a reservoir after the exposure, and then, after opening and closing the chamber, to pump the air out of the chamber before re-admitting the sensitive gas.

The mostserious difficulty with this solution isthe electrical breakdown which occurs when the chamber is pumped out after the exposure. The voltage required for breakdown decreases as the pressure islowered, and at pressures below one atmosphere the electrical potential from the charge deposited during theimaging process can be large enough to permit breakdown between the receptor surface and the electrode opposite the receptor. This electrical breakdown of the gas can completely obliterate the image.

. when the pressure in front of the receptor is reduced below the pressure of the gas behind the receptor. It is known from experience with this problem that if the front of the receptortouches the opposing electrode,

there will be a number of small spots on the pictures, even if the touching occurs during the pump-out before the exposure. In addition the time required for the pump-out can be undesirably long.

Another solution to the problem of moving the receptor in and out without losing the imaging chamber gas is to move the receptor through a close-fitting slot. If the gas pressure is reduced to precisely one atmosphere before the receptor transfer operation, one might hope that the only loss of gaswould be the predictable loss associated with the viscous interaction between the moving receptor surface and the gas in the narrow clearance space. However, the effect of gravity on the heavy gas increases the loss appreciably, and long experience with the system has taught that dust particles caught at the slot exit leave streaks on the exposed image. In addition the effects of electrical breakdown between the charged receptor and theslot edge have been observed. This breakdown occurs even though the slot edge is made of an insulatingmaterial.

Liquid-seals and roller seals at the imaging chamber have also been considered. Another approach to the problem has been to use a flushing gas for flushing air from the imaging chamber afterloading and for flushing the imaging gas from the chamber to a recovery system after exposure. In this approach, the imaging gas is used to flush the flushing gas from the chamber prior to'the exposure, with the gas mixture going to the recovery system. This system has the disadvantage of requiring separation of the flushing gas and the imaging gas in order to recover the imaging gas, and also requiring a gas compressor forpumping the imaging gas to the working pressure in the imaging chamber, which requires some period of time.

All of these proposals have disadvantages and. itis'an object of the present invention to provide a new and improved process and apparatus for handling the high pressure imaging gas in an electronradiography imaging chamber. The invention contemplates the use of flushing liquid to flush air from the imaging chamber after loading and use of the flushing liquid to flush the imaging gas from the chamber to high pressure storage after exposure. The imaging gas is used to flush the flushingliquid from the chamber prior to the exposure,

with the liquid going to a liquid reservoir. The flushing liquid is separated from the imaging gas while at high pressure, eliminating-the need for an imaging gas compressor andeliminating the time'normally required in pumping up to the working pressure in theimaging chamber. Other objects, advantages, features and resultswillmore fully appear in the course of the following description. The single figureof the drawing illustrates an electronradiographic system incorporating the presently preferred embodiment of the gas handling apparatus of the invention.

X-rays are directed from a source 10 past the object 11 being x-rayed to the imaging chamber 12, which may be conventional in design such as set out in the aforementioned copending application. A typical imaging chamber includes a housing 13 carrying an electrode 14 on an insulator 15, with another electrode 16 carried on the housing cover 17. The dielectric sheet receptor 18 may be carried on the electrode l6, with imaging gas being introduced into the chamber at a port 19 filling the gap between the electrodes. The chamber is provided with another port 20 for fluid flow through the chamber. A field is produced across the gap-by an electrical power supply 21 connected across the electrodes.

A supply of the imaging gas, typically xenon, is stored at high pressure in a reservoir 24 and is connected to the port 19 through a flow regulator 28 and a three way valve 26. The imaging chamber port 19 is vented to the atmosphere or other exhaust through a valve 27.

A flushing liquid is stored in a reservoir 30 and is connected to the port 20 through a pump 31. The flushing liquid-preferably is an electrical nonconductive liquid vated charcoal. The flushing liquid collected in the vapor collector may be periodically disposed of or may be returned to the liquid reservoir through a line with valve 36. The imaging gas is returned to the reservoir 24 through a line 37 with a valve 38.

Another gas under pressure may be connected to the port 19 through a valve 40. Typically this source comprises a bottle 41 of compressed air connected to the valve through a needle valve 42 which provides a control for rate of flow. A gauge 44 may be connected to the imaging chamber to provide an indication of chamber pressure if desired.

In operation, a new receptor sheet 18 is place in the imaging chamber and the chamber is closed. Valves 26 and 40 are closed and the vent valve 27 is opened. A pump 31 is actuated to pump the flushing liquid into the chamber, displacing the air through the valve 27. When all the air has been flushed from the chamber, the valve 27 is closed and the pump 31 shutoff. The valve 26 is now opened introducing the pressurized imaging gas into the chamber, displacing the flushing liquid which is returned to the reservoir 30, with the liquid flowing through the stationary pump 31 or through a by-pass line (not shown). The imaging chamber is now charged with the imaging gas at the pressure determined by flow regulator 28, and is ready for x-ray exposure.

After the x-ray exposure, the pump 31 is again actuated to pump the flushing liquid into the chamber, displacing the imaging gas which is returned to the reservoir 24 through the valve 26, vapor collector 25 and valve 38. The valve 26 is then closed and the flushing liquid is removed from the chamber. This may be accomplished by opening the vent valve 27 and reversing the pump 31. Alternatively, the flushing liquid may be displaced from the chamber by opening valve 40 and using the compressed air or other pressurized gas in the tank 41. After the liquid has been removed from the chamber, the chamber may be opened to remove the exposed receptor sheet and insert a new receptor sheet.

In this system, there is no loss of imaging gas. Also, there is no contamination or dillution of the imaging gas, as it is contacted only by the flushing liquid which may be removed in the vapor collector. Further, the imaging gas can remain at high pressure throughout the operating cycle, eliminating the need for any imaging gas compressor and also eliminating the time normally required to pump up the desirable high pressure in the imaging chamber prior to the x-ray exposure.

We claim:

1. In a gas handling system for an electronradiographic imaging chamber having spaced electrodes with a gap therebetween for an imaging gas and having first and second ports for fluid flow through said gap, the combination of:

a first source of imaging gas under pressure;

a reservoir having a flushing liquid therein;

first valve means for connecting said first port to exhaust;

second valve means for connecting said first source of imaging gas to said first port;

a vapor collector connected between said first source and said second valve means; and

a pump for connecting said reservoir to said second port;

whereby said chamber is flushed to exhaust by flushing liquid by opening said .first valve means with said second valve means closed and with said pump in operation, and said chamber is charged with imaging gas by opening said second valve means with said first valve means closed, and imaging gas is flushed by flushing liquid from said chamber to said first source through said vapor collector by opening said second valve means with saidfirst valve means closed and operating said pump, and flushing liquid is separated from imaging gas in said vapor collector.

2. A system as defined in claim 1 wherein said pump is operative to pump flushing liquid from said reservoir to said chamber and to pump flushing liquid from said chamber to said reservoir.

3. A system as defined in claim 1 including:

a second source of flushing gas under pressure; and

third valve means for connecting said second source .to said first port;

whereby flushing liquid is flushed from said chamber to said reservoir by opening said third valve means with said first and second valve means closed.

4. A system as defined in claim 1 including a line connecting said vapor collector to said reservoir for returning separated liquid from said vapor collector to said reservoir.

5. A process of providing imaging gas under pressure to an imaging chamber of an electron radiographic system, including the steps of:

loading a receptor sheet into the imaging chamber;

flushing air from the imaging chamber by means of flushing liquid under pressure; flushing the flushing liquid from the imaging chamber by means of imaging gas under pressure;

retaining imaging gas in the chamber at increasedpressure; exposing said receptor to imaging X-ray radiation,

from the imaging chamber to storage under pressure by means of flushing liquid under pressure; removing the flushing liquid from the imaging chamber; and

unloading the receptor sheet from the imaging chamber.

6. The process as defined in claim 5 including separating the flushing liquid from the imaging gas after flushing from the imaging chamber leaving the imaging gas under pressure for recycling to the imaging chamber.

7. The process as defined in claim 5 including removing the flushing liquid from the imaging chamber by pumping.

8. The process as defined in claim 5 including removing the flushing liquid from the imaging chamber by flushing by means of a flushing gas under pressure. 

1. In a gas handling system for an electron-radiographic imaging chamber having spaced electrodes with a gap therebetween for an imaging gas and having first and second ports for fluid flow through said gap, the combination of: a first source of imaging gas under pressure; a reservoir having a flushing liquid therein; first valve means for connecting said first port to exhaust; second valve means for connecting said first source of imaging gas to said first port; a vapor collector connected between said first source and said second valve means; and a pump for connecting said reservoir to said second port; whereby said chamber is flushed to exhaust by flushing liquid by opening said first valve means with said second valve means closed and with said pump in operation, and said chamber is charged with imaging gas by opening said second valve means with said first valve means closed, and imaging gas is flushed by flushing liquid from said chamber to said first source through said vapor collector by opening said second valve means with said first valve means closed and operating said pump, and flushing liquid is separated from imaging gas in said vapor collector.
 2. A system as defined in claim 1 wherein said pump is operative to pump flushing liquid from said reservoir to said chamber and to pump flushing liquid from said chamber to said reservoir.
 3. A system as defined in claim 1 including: a second source of flushing gas under pressure; and third valve means for connecting said second source to said first port; whereby flushing liquid is flusHed from said chamber to said reservoir by opening said third valve means with said first and second valve means closed.
 4. A system as defined in claim 1 including a line connecting said vapor collector to said reservoir for returning separated liquid from said vapor collector to said reservoir.
 5. A process of providing imaging gas under pressure to an imaging chamber of an electron radiographic system, including the steps of: loading a receptor sheet into the imaging chamber; flushing air from the imaging chamber by means of flushing liquid under pressure; flushing the flushing liquid from the imaging chamber by means of imaging gas under pressure; retaining imaging gas in the chamber at increased pressure; exposing said receptor to imaging X-ray radiation, from the imaging chamber to storage under pressure by means of flushing liquid under pressure; removing the flushing liquid from the imaging chamber; and unloading the receptor sheet from the imaging chamber.
 6. The process as defined in claim 5 including separating the flushing liquid from the imaging gas after flushing from the imaging chamber leaving the imaging gas under pressure for recycling to the imaging chamber.
 7. The process as defined in claim 5 including removing the flushing liquid from the imaging chamber by pumping.
 8. The process as defined in claim 5 including removing the flushing liquid from the imaging chamber by flushing by means of a flushing gas under pressure. 